Flangeless support structures

ABSTRACT

A flangeless assembly for connecting tubular sections of a tubular support structure. A flangeless finger plate assembly connects adjacent tubular sections of a tubular support strucure. The finger plate assembly includes an outer finger plate, an inner finger plate, and corresponding ends of the adjacent tubular section butted at a point. Throughhole arrays are provided on each finger plate such that one throughhole array connects to a matching throughhole array on the corresponding end of the adjacent tubular section. Fastening means are provided to connect the inner and outer finger plates to the adjacent tubular sections according to the throughhole array.

BACKGROUND OF THE INVENTION

The invention relates generally to tubular structures and morespecifically to flangeless connections between sections of tubularsupport structures.

Tubular support structures have many and varied types of application.Some types of support structures exist where equipment is supported atelevated heights from the ground. These support structures may be talland carry operating equipment of various weights at the top, therebysubjecting joints in these structures to high stress. The supportstructures may be used in many applications, including cellular phonetowers, radar towers, and wind towers.

Wind turbine support towers are large structures, sometimes extending tosignificant heights to accommodate large wind turbine rotor blades andto strategically place the rotor blades within a wind path. For example,a typical tower may have a height of about 80 m.

FIG. 1 illustrates an exemplary tubular structure fabricated withtubular sections of welded segment assemblies with flanges welded on theends of the tubular sections. The tubular structure 10 may be built upfrom tubular sections 15, with flanges 27 and 29 on opposite ends thatare bolted together to develop the structure height. The tubularsections 15 include tubular segments 20 of annular shape, also called“cans”. Weld grooves are provided on either the inner or the outer endsurfaces of the tubular segments 20. The tubular segments 20 are weldedto each other in can/can welds 40 to form segment assemblies 25. Thesegment assembly 25 then has a top closure flange 27 and a bottomclosure flange 29 welded to the ends of the segment assembly, using asubmerged arc welding process, a high heat input process. The topclosure flanges 27 and the bottom closure flanges 29 are also annular inshape. The top closure flange 27 and the bottom closure flange 29 ofadjacent sections 15 are then bolted together along a bolt line 30 toassemble the sections together. A base flange 33 at the bottom of thetubular structure 10 and a platform flange 35 at the top of the tubularstructure 10 complete the vertical layout of the structure.

The tubular structure 10 of FIG. 1 may represent a typical wind towerfor supporting a wind turbine or other various kinds of support towers.For this exemplary tower of about 80 m in height, the tower includesthree sections, two sections being about 25 m long and one section beingabout 30 m long. The length and number of individual sections in otherrepresentative tubular structures may vary according to the applicationand height of the structure. The tower may be either cylindrical orconical.

For example, a tower height of 50 meters may be employed for high windconditions and 110 meters for low wind conditions. The horizontal crosssection of the exemplary tower is generally circular and may be taperedat upper levels. Tapering may be achieved by use of individual tubularsegments, the tubular segments tapered as right conical sections alongan axial direction. However, the horizontal cross section for thetubular segments of other representative structures may be of differentgeometries.

FIG. 2 illustrates a cross-sectional view of a properly aligned flangeconnection for sections of a tubular structure. The flange/can weld 37connects the top closure flange 27 with the segment assembly 25 locatedbeneath it. The flange/can weld 39 connects the associated bottomclosure flange 29 with the welded segment assembly 25 located above it.Ideally, the flange mating surface 41 of the top closure flange 27 andthe flange mating surface 43 of bottom closure flange 29 should becompletely parallel for the throughhole 45 intended for bolt 47 and nuts49 to be perfectly aligned with both flanges.

On-going problems with the exemplary wind turbine support tower includeweld cracking, flange distortion and bolt failure during tower flexure,each contributing to the life cycle cost of the tower. Moreover, theheat generated during the flange welding process distorts the flanges.

FIG. 3 illustrates a process for bolting with a distorted flange.Initially, due to the heat applied at the flange to can weld joint, theflange 29 is distorted in A. When a welded top flange 27 and a weldedbottom flange 29 are brought together, the bolt lines of thethroughholes 45 are misaligned in B and the tubular sections 15 (FIG. 1)are thus capped by distorted flanges. Bolts 47, used to join adjacentflanged modules 15, may be torqued until the deformed flanges arebrought into alignment in C. These bolts 47 with nuts 49 may be torquedto a pre-stress level, for example about 590 Mpa, allowing the deformedflanges to be brought into alignment. This operation develops highprestress in both the welds 37 and 39 and the bolt 47, reducing thecapacity to sustain service-induced loads. Such high and non-uniformprestresses in the bolts may lead to bolt failures and weld failures inD. Similar problems may also be encountered in other types of tubularsupport structures with similar welded flanged joints.

Welds, by nature, have inherent stress concentration features. Whentubular structures, such as towers are subjected to high wind loads, thetower experiences flexural stresses. Superimposed on theses are highcycle vibration flexural stresses driven by the mass at the top of thetower. This combination of factors, in addition to the pre-stressing ofassembly, places high tensile stresses on the welds and bolts leading toa high probability of weld cracking or bolt failure with the associatedhigh maintenance costs. Bolt failure has become such a significant issuethat suppliers have to machine the flange after welding to meet theflatness requirement Some tower requesters, for example, may require thesupplier to measure flange flatness using a laser measurement, withanything in excess of 1.5 mm deviation from planar requiring furthermachining. A supplier may have to cut and re-weld flanges to meet thisrequirement. This may have a major impact on cost and schedule, as wellas tower strength.

An additional area of concern is the flange weld inspection. It isdifficult to get an accurate assessment of weld integrity sinceprevailing inspection techniques rely on a calibrated, non-direct,detection procedure.

Accordingly, there is a need to provide an assembly for wind turbinesupport tower modular sections that do not result in high stress in theconnecting joints and which allow the stresses to be checked.

BRIEF DESCRIPTION OF THE INVENTION

The present invention relates to in general to a joint for joiningsections of a tubular structure together, and in particular to aflangeless joint for joining sections of a wind turbine support tower.

Briefly, one aspect of the invention provides a finger plate assemblyfor connecting two adjacent tubular sections of a tubular supportstructure. The finger plate assembly includes an outer finger plate; aninner finger and corresponding ends of the adjacent tubular sectionsbutted at a point. Throughhole arrays are provided on each finger plate,where each throughhole array provides connection to one of the twoadjacent tubular sections. A matching throughhole array is located onthe corresponding ends of the adjacent tubular sections. Means forfastening the inner and outer finger plate to the tubular sections isprovided.

Briefly, in accordance with another aspect of the present invention, aflangeless joint is provided for connecting two sections of a tubularsupport structure. The flangeless joint includes two adjacent sectionsof the tubular support structure and a plurality of finger plateassemblies uniformly distributed around the periphery of the twoadjacent sections of the tubular support structure.

Briefly, in accordance with a third aspect of the present invention, atubular support structure is provided. The tubular support structureincludes a plurality of tubular sections and a plurality of flangelessjoints employing finger plate assemblies for connecting adjacent tubularsections, the finger plate assemblies being uniformly distributed aroundthe periphery of the adjacent tubular sections.

BRIEF DESCRIPTION OF THE DRAWING

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 illustrates an exemplary tubular structure with flanged sectionsthat are bolted together.

FIG. 2 illustrates a cross-sectional view of a properly aligned flangeconnection for modular sections of a tower;

FIG. 3 illustrates a process for bolting with a distorted flange;

FIG. 4 illustrates a side sectional view of an finger plate assembly;

FIG. 5 illustrates an isometric view of a typical finger plate;

FIG. 6 illustrates the relative stiffness of a finger plate assemblyjoint and a current short flange joint in response to tower sidesway;

FIG. 7 illustrates the flangeless joint utilizing finger plateassemblies uniformly distributed around the periphery of a tubularsupport structure;

FIG. 8 illustrates an axial cross section of a wind turbine supporttower including flangeless joints connected with finger plateassemblies.

DETAILED DESCRIPTION OF THE INVENTION

The following embodiments of the present invention have many advantages,including avoidance of high tensile stresses on welds and bolts leadingto a probability of weld cracking or bolt failure and the associatedhigh maintenance costs.

One aspect of the present invention provides finger plate assemblies tojoin adjacent sections of a tubular assembly. FIG. 4 illustrates a sidesectional view of a finger plate assembly 50 that overcomes thepreviously described problem, in tubular assemblies with welded flangedjoints, of flange distortion after welding. The annular rings of twoadjacent flangeless modular sections 52 and 54 of the tubular assembly(without flanges) are brought together in close proximity at point 56.An inner finger plate 57 is provided on an interior of the tubularassembly. The inner finger plate 57 may be provided with a curved outerdiameter matched to the curved inner diameter of the flangeless modularsections 52 and 54. The inner finger plate 57 is provided for connectingthe inner surfaces 58 and 60 of the adjacent flangeless sections. Anouter finger plate 62 is provided on an exterior of the tubularassembly. The outer finger plate 62 may be provided with a curved innerdiameter matched to the curved outer diameter of the modular sections 52and 54. The outer finger plate 62 is provided for connecting the outersurfaces 64 and 66 of the adjacent flangeless modular sections.Fastening throughhole arrays are provided on each finger plate and arematched with the fastening throughhole array provided on thecorresponding adjacent ends of the flangeless modular sections. Theassembly further may further include bolts 47 and nuts 49 according tothe throughhole array. However, other suitable fastening means may beutilized depending upon the particular application.

FIG. 5 illustrates an isometric view of a typical finger plate utilizingnut and bolt fastening. The typical finger plate 70 has an inner surface72 and an outer surface 74. For an inner finger plate, its outer surfaceis matched to the curved outer surface of the adjacent tubular sections.For an outer finger plate, its outer surface matched to correspondingsurface of adjacent tubular sections. A typical bolt throughhole array76 is shown for connection with one tubular section and typical boltthroughhole array 78 is shown for connection with the adjacent tubularsection. Finger plate design is according to standard design practiceincluding spacing of bolt throughholes from the edge of the fingerplate, spacing between adjacent bolt throughholes, thickness of thefinger plate, surface dimension of the finger plate and plate materialselection.

For the exemplary 80 m tower, the finger plate may have an arc dimensionof about 2 m, a height of about 1 m, and a thickness of about 30-40 mm.The material for finger plates may preferably include ASTM A 572 Gr 50steel plate. Bolt throughhole arrays 76 and 78 on the finger plates maybe preferably configured in double rows applied to each adjacent sectionof tower for a total of about 48 bolt holes per finger plate. Diameterfor the bolt throughholes may preferably be sized about 1.25 inch.Minimum spacing between the bolt throughholes may be about 5 inches.Typical bolts for the finger plates in the 80 m tower may preferably beM36 10.9 grade bolts that are torqued to a bolt prestress of about 510Mpa (74 ksi).

In addition to eliminating the end flanges, the discrete natureaccommodates slight aberrations in tower section geometry to speed upassembly and minimize expensive re-work. The finger plate assemblies aredesigned with sufficient thickness, length and width to provideacceptable local and overall stiffness to address tower side-sway andstability requirements. Standard bolt design practice will determinefinger plate dimensions.

FIG. 6 illustrates the relative stiffness of a finger plate assemblyjoint and a current short flange joint in response to tower sidesway.Long curved finger plate assembly joint 80 of inner finger plate 57 andouter finger plate 62 provide increased joint stiffness for resistingbending due to tower sidesway. The finger plate assembly joint 80distributes the bending moments over a longer curved surface L1 ascompared to a short surface L2 of top closure flange 27 and bottomclosure flange 29 available to absorb the sideway moment in theconventional flanged joint 85.

A typical flangeless joint with finger plate assemblies according to oneaspect of the present invention uniformly distributes a plurality offinger plates around the periphery of adjacent sections of the tubularsupport structure.

FIG. 7 illustrates a flangeless joint 90 with finger plate assemblies 92uniformly distributed around the periphery of a lower tubular section96. The inner finger plates 93 and outer finger plates 94 and the lowertubular section 96 are shown for clarity. An upper tubular structure andfasteners are omitted for the sake of clarity. The tubular structure maybe a support tower or a wind turbine support tower. For an exemplarywind turbine support tower of about 80 m, five finger plate assembliesmay be distributed around the periphery of the adjacent sections of thewind turbine support tower. Further bolting may be employed as afastening means for the wind turbine support tower. While a simplifiedscheme for bolting throughholes is shown, FIG. 5 illustrates a fingerplate with a more typical throughhole array for the exemplary windturbine support tower.

The curved nature of the finger plates contributes to joint stiffness.Appropriate design of the finger plate length, thickness, and width willstiffen the joint locally and provide prescribed over-all towerstiffness for side sway, stability, and tower-head eccentric loading ina much more structurally efficient manner compared to flanged joints ofprior art. The thickness and spacing of the finger plates will also be afunction of the prevailing standard practice for bolted joint design.The bolt hole diameter and spacing will be a function of serviceconditions.

The use of finger plate assemblies replaces welding flanges to the canassemblies as the means of joining modular sections of the tower.Consequently, the distortion and prestressing problems associated withthese welds and the bolts is eliminated. Further, it is difficult to getan accurate assessment of weld integrity since prevailing inspectiontechniques rely on a calibrated, non-direct, detection procedure.Replacing the welds with bolts allows an inspector to check each boltfor allowable pre-load using a torque wrench.

According to yet another aspect of the present invention, a tubularstructure is provided that includes a plurality of tubular sections anda plurality of flangeless joints employing finger plate assemblies forconnecting the adjacent tubular sections. The finger plate assembliesare uniformly distributed around the periphery of the adjacent tubularsections. The tubular structure may define a support tower and morespecifically a wind turbine support tower that utilizes the finger plateassemblies for joining modular sections of the tower. The modularsections of the tower are assembled by welding tubular segments to formtower sections.

FIG. 8 illustrates an axial cross section of a wind turbine supporttower 105. The wind turbine support tower 105 incorporates flangelessjoints 90 utilizing finger plate assemblies 120 for connecting towersections 96. The wind turbine support tower 105 provides support forwind turbine generator 110 and wind turbine rotor 115. The exemplarywind turbine support tower 105 is about 80 m in height, incorporatingthree tower sections 96 and two flangeless joints 90.

In this exemplary wind turbine support tower, five finger plateassemblies may be uniformly distributed around the periphery of theflangeless joint. The tower sections may be cylindrical shaped or have agenerally truncated right conical section to provide for overallreduction in cross section of tower sections at higher elevations.Further individual tubular segments may be individually tapered alongthe axial length to provide for the progressive reduction in crosssection for each individual tower section along the axial length of thetower section.

While only certain features of the invention have been illustrated anddescribed herein, many modifications and changes will occur to thoseskilled in the art. It is, therefore, to be understood that the appendedclaims are intended to cover all such modifications and changes as fallwithin the true spirit of the invention.

1. A finger plate assembly for connecting two adjacent tubular sectionsof a tubular support structure, the finger plate assembly comprising: anouter finger plate; an inner finger plate; corresponding ends of theadjacent tubular sections butted at a point; throughhole arrays on eachfinger plate, wherein each throughhole array provides connection to oneof the two adjacent tubular sections; a matching throughhole arraylocated on the corresponding ends of the adjacent tubular sections; andmeans to fasten the inner and outer finger plates to the adjacenttubular sections.
 2. The finger plate assembly as claimed in claim 1,wherein horizontal cross-section of tubular sections arecircular-shaped.
 3. The finger plate assembly as claimed in claim 2,wherein: the outer finger plate comprises a plate curved inner diametermatched to a curvature of an outer surface of the tubular sections; andthe inner finger plate comprises a plate with a curved outer diametermatched to a curvature of an inner surface of the tubular sections. 4.The finger plate assembly as claimed in claim 3, wherein the tubularsections comprise sections of a support tower.
 5. The finger plateassembly as claimed in claim 3, wherein the tubular sections comprisesections of a wind turbine support tower.
 6. The finger plate assemblyas claimed in claim 1, wherein bolts and nuts comprise the means forfastening according to the throughhole array.
 7. The finger plateassembly as claimed in claim 1, wherein the throughhole array issymmetric with respect to the adjacent tubular sections of the tubularsupport structure.
 8. The finger plate assembly as claimed in claim 1,wherein the throughhole arrays on the inner finger plate, the outerfinger plate, and the adjacent ends of the tubular sections are machinedprior to assembly of finger plate assembly.
 9. A flangeless joint forconnecting two sections of a tubular support structure, the flangelessjoint comprising: two adjacent sections of the tubular supportstructure; a plurality of finger plate assemblies uniformly distributedaround the periphery of the two adjacent sections of the tubular supportstructure.
 10. The flangeless joint for connecting two sections of atubular support structure as claimed in claim 9, wherein the twoadjacent sections of the tubular support structure comprise sections ofa support tower.
 11. The flangeless joint for connecting two sections ofa tubular support structure as claimed in claim 10, whereincross-sections of the adjacent sections of the tubular support structureare circular-shaped.
 12. The flangeless joint for connecting twosections of a tubular support structure as claimed in claim 11, whereinthe two adjacent sections of the tubular support structure comprisesections of a wind turbine support tower.
 13. The flangeless joint forconnecting two sections of a tubular support structure as claimed inclaim 12 wherein five finger plate assemblies are uniformly distributedaround the periphery of the adjacent sections of the wind turbinesupport tower.
 14. The flangeless joint for connecting two sections of atubular support structure as claimed in claim 13, wherein the uniformlydistributed finger plate assemblies employ bolting as a fastening means.15. A tubular support structure comprising: a plurality of tubularsections; and a plurality of flangeless joints employing finger platesassemblies for connecting adjacent tubular sections, the finger plateassemblies being uniformly distributed around the periphery of theadjacent tubular sections.
 16. The tubular support structure as claimedin claim 15, wherein the tubular support structure comprises a supporttower.
 17. The tubular support structure as claimed in claim 16, whereinthe support tower comprises a wind turbine support tower.
 18. Thetubular support structure as claimed in claim 17, wherein the flangelessjoints further comprise five finger plate assemblies uniformlydistributed around the periphery of adjacent tubular sections.
 19. Thetubular support structure as claimed in claim 18, wherein the windturbine support tower further comprises: a base supporting the tower;tower sections joined by the flangeless joints; a platform connected tothe top of the modular sections; and a wind turbine and wind turbinerotor supported on the platform section.
 20. The tubular supportstructure as claimed in claim 18, wherein the tower sections furthercomprise modular sections of welded tubular segments.